I tried to install Vivaldi, unfortunately it requires SDK 21, but the SDK version on Xperia X is 19. Vivaldi is my favourite browser on desktop.
Back to the question of @PatsJolla
I use Lightning browser, it works more or less at the same speed as stock browser only some sites are being rendered better than on stock browser.Also for some sites purely for reading longer articles without distractions Lelig web works very well.
Otherwise being in a limbo and waiting for updated stock browser or updated Qt, what will empower Webcat and Webpirate, o probably bring other browsers native ports.